1. Field of the Invention
The present invention relates in general to flow stoppage detectors for particulate material supply lines and, more specifically, to such detectors that are adapted to stop a further delivery of material to the supply line when the supply line becomes obstructed.
2. Description of the Prior Art
Various prior art devices have been employed in association with a supply line for monitoring the flow of material through the line as exemplified by U.S. Pat. No. 2,907,015; Jackson, U.S. Pat. No. 2,654,879; Waters, et al., U.S. Pat. No. 2,561,763; Bogot, et al., U.S. Pat. No. 2,659,881 and Donner, U.S. Pat. No. 410,502. The above patents disclose devices having electrical switch means with switch arms disposed in the normal path of the flow of material, and all of the devices, except that of Donner, operate in direct response to such flow. The Donner device operates in response to a back-up of material in the supply line to actuate a switch arm and sound an alarm.
Although the above devices appear to be useful for their intended purposes, mounting of a switch arm in the direct flow path of material in the supply line is highly undesirable since the switch arm is continuously acted upon by the material flow and is difficult to maintain free from dust and contaminates that collect thereon from the material flow.